Again, you have to read the law. Each nation has its own out look on the situation. Carlos Salinas Gotari, former president of Mexico, took asylum in Ireland. His enemies blamed him for all of the economic ills. They prevented his daughter from having Mexican citizenship. She has to carry and Irish passport.
Guess what? EVERY NATION HAS ITS OWN OUTLOOK on the situation. The US is not responsible for fixing all of the injustices in the world, nor should it be. If enough Mexicans don't like things the way they are in Mexico, and they can't conveniently move to the US illegally, maybe they will get around to improving things in Mexico. There is no reason that we should fix any nation's domestic problems by providing an escape valve for foreign nationals.
Let's just mirror back to other countries what their laws say. Problem solved. No welfare for children of foreigners in Mexico; no welfare in US for children of Mexicans living in the US. No birthright citizenship in China or Japan; no birthright citizenship for Chinese or Japanese nationals children in the US.